Various types of rear loading trailers have been proposed to facilitate the unloading and/or loading of equipment, particularly heavy equipment.
One type of trailer is designated by the reference numeral 10 in FIG. 1. This trailer represents an off-the-road heavy equipment trailer having a trailer body 11 and a gooseneck hitch 13, the hitch 13 designed to attach to a hauling vehicle. The rear end 14 of the trailer includes at least a pair of wheels 15 that are mounted on an axle 17. A ramp 19 permits loading or unloading of heavy equipment onto the trailer body 11. The ramp 19 can be raised using hydraulics or the like.
FIG. 2 illustrates a second type of rear end loading trailer designated by the reference numeral 20. This trailer has a trailer body 21, a trailer hitch 23, and two sets of rear wheels 25, each set mounted on axles 27. Rear loading of the trailer 20 is accomplished by attachment of a ramp 29 to the rear end portion 24 of the trailer. The ramp is connected at reference number 28 using conventional means.
The rear end loading trailers depicted in FIGS. 1A and 1B are not without their disadvantages. Referring now to FIG. 1C, a piece of heavy equipment 31 is illustrated being loaded onto a trailer 33. The trailer gooseneck 35 is shown attached to a hauling vehicle 37. During loading, the entire weight of the heavy equipment 31 is supported only by the rear axles and/or wheels 38. Only when the heavy equipment 31 is seated for traveling between the wheels 38 and gooseneck hitch 35 is the load distributed between the front and the back of the trailer. During this overloading, the rear tires can be overloaded up to 200% of their normal loading. Such overloading causes the tires to flatten out and can result in damage to the tires and/or axle. Moreover, depending on the height of the trailer, the ramps attached to the rear end have to be rather long to ensure a gradual ramp angle. Alternatively, as shown in FIG. 1B, the ramp angle may be steep due to a relatively short ramp, such a steep ramp angle contributing to instability during a loading or unloading procedure.
Trailers having vertical lift or drop frames have also been proposed in the prior art. U.S. Pat. No. 3,811,697 to Armstrong discloses a vertical lift trailer having a pair of ground engaging wheels on opposite sides of the frame. Each wheel has an axle and a supporting arm connected at one end to each axle respectively and extending forwardly therefrom. Means swingably connecting the other ends of the supporting arms to the frames are provided for swinging movement about the transverse axis thereby to shift the wheels between lowered and elevated positions relative to the frame. U.S. Pat. No. 4,077,643 to Bates discloses a utility trailer with a frame which may be lowered to ground level at both the front and rear portions of the trailer to permit easy access and to facilitate loading and unloading of heavy vehicles and other items. The trailer frame is attached to a u-shaped axle which, in turn, is connected to a wheel suspension support. The wheel suspension may be raised or lowered by rotation of the wheels' suspension about the axle allowing the rear of the trailer frame to be raised or lowered. The front of the trailer frame is connected to a cable controlled by a winch which will pivot for lowering or raising of the front part of the trailer frame. Locking pins are employed to lock the suspension and the front portion of the trailer frame in place during travel. Neither of these patents teach or suggest a mechanism for off-the-road trailers nor the utilization of a ramp in concert with a trailer body to facilitate loading/unloading.
In light of the deficiencies in prior art rear loading trailers, both off-the-road and on-road, a need has developed to provide an improved trailer. The present invention solves this needs with the development of a rear loading trailer having a mechanism which simultaneously provides ramp access to the trailer body while lowering the trailer body onto a ground surface. In this way, separate ramp manipulations or systems are eliminated.